1. Field of the Disclosed Embodiments
This disclosure relates to systems and methods for waste ink continuous filtration in liquid ink image forming or production devices, including and particularly to a waste ink filtration system and method that continuously filters ink and/or skin out of cleaner waste fluid and cleans the filters without disruption in the liquid ink image forming or printing process.
2. Related Art
Digital printing is generally understood to refer to systems and methods in which images may be varied among consecutively printed images or pages. “Variable data lithography printing,” or “ink-based digital printing,” or “digital offset printing” are terms generally referring to printing of variable image data for producing images on a plurality of image receiving media substrates, the images being changeable with each subsequent rendering of an image on an image receiving media substrate in an image forming process. “Variable data lithographic printing” includes offset printing of ink images generally using specially-formulated lithographic inks, the images being based on digital image data that may vary from image to image, such as, for example, between cycles of an imaging member having a reimageable surface.
“Ink-based digital printing” or “digital offset printing” systems and methods may include an ink jetting process in which a piezoelectric ink jet print head may be used to apply ink to an imaging member, in particular, an intermediate transfer component (e.g., roll, drum, belt). The jetted ink may be disposed on a pre-coat layer of liquid solution commonly be referred to as “skin”, which may primarily consist of a combination of a starch, a surfactant and water. Skin may also consist of a combination of starch, a surfactant and glycerin. In particular, skin is also known in the form of a partially dried mixture of polymeric binder, liquids and release agent, such as oil, that is capable of supporting the printed intermediate image for subsequent transfer to an image receiving media substrate. The skin layer may require different levels of drying prior to suitability to apply the jetted ink. The intermediate image is transferred by contact between a surface of an intermediate transfer component and the image receiving media substrate, typically with the assistance of a pressure roller or drum to create a transfer nip.
In these variable data lithography printing systems, ink-based digital printing systems, and digital offset printing systems, which are also referred to hereinafter as variable data ink-based printing systems or variable data ink-based image forming devices, the printing surface supports an image that is only printed once and is then refreshed. These systems require cleaning subsystems at the intermediate transfer component after the transfer nip to continuously remove post transfer residual ink and/or skin from the reimageable surface of the intermediate transfer component prior to formation of the next print image and to avoid ghosting. The cleaning subsystems use a cleaning solution to aid in removal of the transfer residual ink and/or skin. During the printing process, waste stream of dilute ink and/or skin in cleaning solution continuously flows from the cleaner housing. For safety and environmental reasons, the ink and/or skin must be properly disposed, typically under contract with a printing waste disposal company to collect and dispose of the printing waste materials. These contracts are expensive and can interrupt the printing process. The inventor recognized the need for a more economical approach.
The need to filter a waste fluid stream does not exist with traditional printing technologies. In traditional printing technologies the printing surface contains a static image that generates many prints. It doesn't matter if some ink fails to transfer from the printing surface to the print media on the first pass, because the same image will appear on all of the prints. Cleaning of the printing surface in traditional printing is not continuous. Cleaning is done when the printing press is shut down. Some automatic cleaning systems are available to clean the printing surface, but cleaning is still done while the press is stopped. The waste materials from these cleaning operations need to be disposed of properly, but the volume of waste is much smaller than in a continuously cleaning processes of variable data ink-based image forming devices, which print variable images that can change from one print to the next. If the untransferred ink is not removed it may show as a ghost image on the next print with a different image. Accordingly, continuously cleaning the reimageable printing surfaces within variable data lithography printing systems, ink-based digital printing systems, and digital offset printing systems produces a high volume of waste material far greater than intermittent cleaning of traditional printing systems because the printing waste material is generally contained within the flow of cleaning solution.